But it is also correct that the 2,520 years is very off. Jewish years are composed of 12 lunar months of 29.5 days. Every few years a leap month of 30 days is added, but until modern times this did not happen on a set schedule.
If one were to count 2,520 Biblical years from 607 B.C.E. one would need further instructions: do we add leap months, and if so, according to the modern method or the ancient one? And if we use the ancient one, do we match the way the Jews were adding extra months or do we make corrections that we now know they failed to make (which is why we now have a system in place to tell us when we are adding an extra month)?
I was doing this the other night with some rabbinical assistance but had to stop when Shabbat began. We realized that there can thus be three figures, none of which match 2,520 solar years as the count is made by Jehovah's Witnesses to arrive at 1914 C.E.
We always ended up with a discrepancy that kept us about 300 years on average short of the 1914 date. Because the Witnesses count the Gentile Times using solar years, they are like the fictional Germans from the movie, "Raiders of the Lost Ark." Having made a "measuring rod" based on a miscalculation of some Jewish writing, the bad guys in that film were "digging in the wrong place" for The Ark. The same is true for the Bible Students who made up that formula of 7 Gentile Times: even if their 607 starting date is right, and their 2,520 is precise, they counted 2,520 Gregorian calendar years to get to 1914 when they were supposed to be using the lunar years of the Jewish calendar.
1914 is never a possibility using any of the dates on hand for the beginning of the Gentile Times, and there is probably no way to know how to count from then up to now because of the leap year issues.
